Data were collected to determine concentrations of major ions, nutrients, and selected trace elements in collector drains tributary to the San Luis Drain; the San Luis Drain near Kesterson Reservoir; Kesterson Reservoir; and selected drains, canals, and sloughs near but not tributary to Kesterson Reservoir, California. Results from 14 samples collected during January 24-26, 1984, are summarized in tables, and the sample locations are shown on maps. (USGS)